National Semiconductor Corporation

Toyojiro Naokawa

Hiroshi Hirayama

William H Gross

Katsushige Fujii

Matsuro Koterasawa

An audio amplifier with no turn-on pop noise is achieved by the following features: (i) an input stage which operates under zero common-mode input voltage, (ii) an output stage which provides the low voltage end of its voltage swing very close to ground voltage, and (iii) a system of shunt circuits for discharging external capacitors, so as to prevent, upon subsequent power-up, pop noises due to residue charges in the external capacitors. In one embodiment, two peripheral collector transistors are provided to implement a window comparator for discharging the input terminals, the bias voltage and the output terminal of the audio amplifier.

No turn-on pop noise amplifier

A class AB rail to rail output stage circuit, which includes two complementary output transistors connected in a push-pull manner, facilitates biasing of circuit transistors and improves frequency stability while supporting a wide rail to rail output voltage swing. A differential amplifier compares a biasing voltage applied to a first complementary output transistor to a reference voltage and the differential amplifier output signal is applied for biasing a second complementary output transistor.

Class AB output stage with improved frequency stability

A matrix circuit is disclosed having four inputs for coupling to either the four elements in a four-quadrant photodetector in a one-beam optical disc system or to the six elements in a hex photodetector in a three-beam optical disc system. A fifth input is provided with a logic input determined by which system is being implemented. Three outputs are provided, one each for signal, tracking error and focus error. The circuit will accommodate both systems to produce the required outputs with a minimum of redundant parts.

Matrix circuit for optical disc systems

A peak-to-peak signal detector circuit is disclosed. It can be directly coupled and rejects any d-c component associated with the signal without requiring a coupling capacitor. The input is applied to separate positive and negative peak detectors the outputs of which are subtractively combined in an op-amp. A circuit application as a drop out detector in an optical disc system is detailed.

Direct current coupled peak to peak detector circuit

A current mirror provides an output current, for use in an IC, that is a multiple of a reference current input. A high gain negative feedback loop is coupled between the current mirror reference input and the output device. This forces the reference input to operate as a diode and stabilizes the circuit operation so that the output current accurately reflects the reference current independently of the .beta. of the devices.

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Saitama, Japan

Toyojiro Naokawa